Orthodontic brackets may be used with arch wires to straighten irregular teeth. These brackets are attached to the teeth and engage a flexible arch wire that exerts pressure upon them to move the teeth. The most commonly used brackets are edgewise brackets as shown in FIGS. 1, 2, and 3. FIG. 1 shows a Siamese twin bracket, FIG. 2 shows a single bracket with rotation wings, and FIG. 3 shows a modified edgewise bracket known as Tip-Edge bracket. Such brackets typically include an arch wire slot that extends horizontally across the face of the bracket for the reception of the arch wire. This slot can be angularly oriented to minimize bending of arch wires. A pair of wings extend vertically on either side of the arch wire slot from the bracket enabling ligature means to be tied to the bracket to retain the arch wire in the slot. Stainless steel ligature ties or elastomeric ligature rings are conventionally used as the ligature means.
Placement of these small wires or elastomeric ligature rings requires considerable time during initial installation of an arch wire. It is also normally necessary to remove and replace the ligatures each time an arch wire is changed.
Ligatures also tend to make proper oral hygiene more difficult as the wires can trap food particles, and the twisted ends of a ligature may be shifted during cleaning into a position where irritation of the patient's gums or cheek tissues occurs.
When repositioning teeth with brackets, it is often necessary to cause the teeth and the brackets to slide along the arch wire. Since the ligature ties are in firm contact with the arch wire, friction is generated between the brackets and the arch wire affecting the tooth movements adversely.
Many of these problems presented by ligatures are overcome by self-locking orthodontic brackets. So far numerous attempts have been made to develop such brackets.
U.S. Pat. No. 2,671,964 to Russel et al. that was issued on Mar. 16, 1954 shows a hollow bracket with a slidable cover within. This bracket does not have tie wings that are necessary for engaging elastomeric chains and continuous ligature ties. U.S. Pat. No. 3,131,474 to Johnson also shows a hollow bracket with a slidable cover recessed with in. Both these brackets are hollow and have to be manufactured from metal sheets whereas the contemporary brackets are solid.
U.S. Pat. No. 5,094,614 to Wildman issued on Mar. 10, 1992 discloses a slidable closure that engages the front of the arch wire. The closure is recessed from the front or anterior surface of the disclosed bracket.
U.S. Pat. Nos. 5,275,557; 5,429,500, & 5,466,151 to Damon show a slidable cover supported by sliding guides that engage the opposed side surfaces of tying lugs. A transverse flat spring is recessed within the fixed wall to selectively engage indented areas on the posterior surface of the cover and serve as detent.
Another slidable cover has been disclosed in U.S. Pat. No. 5,322,435 issued to Pletcher on Jun. 21, 1994. A resilient member is provided to retain the slide member of the bracket in either the open or closed position, while preventing excessive sliding movement that could disengage the slide member.
Various other locking means such as a slidable spring cover, a hinged locking cover, a rotary slidable cover, a bail type rotatable cover etc. have been disclosed in different U.S. Patents. "Activa" produced by A Company, "Speed" and "Edgelock" produced by Ormco Corporation, and others are typical examples of ligature-less brackets that are commercially available.
Of all these different locking means a sliding closure is particularly desirable because it can be easily manipulated and it reduce the time required for opening and closing of the arch wire slot during periodic adjustments of the arch wire. It also provides more precise control of the arch wire:. The other means are more complex, however, and therefore difficult and expensive to manufacture Also, they are not as compact as would be desired. Additionally, it is difficult to use auxiliary attachments with brackets without tie wings. Also, with brackets having detachable parts, there are chances of such parts getting separated accidentally and getting lost or swallowed by patients. Moreover, springs used as locking means are not strong enough to hold the arch wire into the slot.